This project focuses on four hypotheses related to early-emerging social communicative mechanisms known to be impaired in individuals with autism: (1) Toddlers (24-36 mo.) with symptoms of autism will show less than typical preference for listening to speech under controlled experimental conditions, as opposed to nonsocial auditory stimuli with analogous acoustic properties. (2) Toddlers with symptoms of autism will show less than typical preference for three prosodic patterns characteristic of their native language: stress patterns in words, pause patterns in sentences, and intonation contours in connected speech. (3) Listening preferences will be correlated with concurrent degree of communicative and social competence and will predict later language and social competence. (4) Listening preferences at 24-36 mo. will discriminate children who meet diagnostic criteria for autism spectrum disorders from those who do not, both concurrently and when diagnosis is confirmed at 48-60 mo. We request 5 years of support to examine these hypotheses in children with autism-related conditions seen at 24-36 mo. (Time 1) and again at 48-60 mo. (Time 2). This group will be matched to a group of children with non-autistic developmental delays and to a group with typical development. For Hypotheses 1 and 2, the preferential head-turn paradigm, a method used for over 20 years in the study of infant auditory perception, will be used to examine group differences in listening preference. For Hypotheses 3, the relationship between these listening preferences and standardized measures of communicative and social competence will be examined at both Time 1 and Time 2. For Hypothesis 4, the predictive power of listening patterns relative to concurrent diagnostic assignment and confirmatory diagnostic group membership two years later will be investigated. Our longer-term goals are to develop these preferential listening paradigms into performance based measures capable of identifying children at risk of having autism in the first year of life, which is an important goal given the proven benefits of early intervention. In addition, the information gained in this study will be used to generate hypotheses regarding appropriate treatment procedures to optimize early listening experience in children with these disorders.